The long-term objective of our program is to develop analytical methods on micromachined platforms for biomedical analytes. The present proposal deals with the separation and preconcentration of selected analytes onto reagents that are tethered to gold electrodes or nanoclusters. The tethering is via molecular self-assembly. Fluorogenic crown ethers will be modified with alkanethiol tags and attached to gold by spontaneous formation of the thiolate. Selective uptake of lithium or potassium ion by the crown will provide the separation step. Release of the entire assembly into a flowing carrier solution by oxidation of the thiolate will be one strategy that will allow quantifying the results at a downstream detector. Prior to the next measurement, the assembly will be re-made or a new electrode will be placed in the system. Alternatives of the basic experiment include other combinations of capture reagent and analyte, e.g. a cyclophane and phenylalanine or adrenaline; tethering reagents to gold nanoclusters embedded in a flow-through silica sol-gel electrode; and chemical release that retains the integrity of the self-assembled monolayer on gold. These systems are designed specifically to be integrated with microchip and micromachined platforms to yield Total Analytical Systems. Applications as disposal devices for selective determinations of analytes in blood are envisioned.